Bioelectric impedance analysis for body composition measurement and other potential clinical applications in critical illness

Abstract

Purpose of review Insight into body composition is of great value in the ICU. Bioelectric impedance analysis (BIA) is the most applicable bedside technique. However, bioimpedance has not been validated in the critically ill, and the interpretation of the measurements poses challenges. This review discusses the potential clinical applications of BIA and explores caveats and solutions to its use in the intensive care setting. Recent findings A correlation is repeatedly found between raw impedance parameters, fluid ratios, overhydration, and adverse outcome of critical illness. However, cut-off and reference values remain elusive. Experience with BIA-guided fluid management in the ICU is limited. BIA-derived muscle mass appears a promising biomarker for sarcopenia, correlating well with CT-analysis. Body cell mass and fat-free mass provide potential use in estimation of metabolic rate, protein requirements and pharmacokinetics. Several methods of reducing bias in BIA parameters in critical illness require validation. Summary There are currently too many uncertainties and discrepancies regarding interpretation of bioimpedance in critical illness, to justify therapeutic consequences. However, there are several promising areas of research, concerning some of the most urgent clinical problems in intensive care, emphasizing the need to evaluate further the use and interpretation of bioimpedance in the intensive care setting.

Bioelectric impedance body composition and phase angle in relation to 90-day adverse outcome in hospitalized COVID-19 ward and ICU patients: The prospective BIAC-19 study

“…Henceforth, the software uses validated methods to estimate fat-free mass (FFM), soft lean mass (SLM), mineral mass, bone mineral content (BMC), percentage body fat (PBF), VFA, skeletal muscle mass (SMM), body cell mass (BCM) and protein mass, in addition to several ratios and segmental values. Fluid overload (FO) was calculated by subtracting a recalculated ECW based on a normal ECW/TBW ratio of 0.380 from the measured ECW (i.e., OH ¼ ECW measured e ((ICW Â 0.380)/0.620)), a method that is used in dialysis patients [1,2].…”

“…A PhA greater than 6 is assumed healthy, although the normal range varies with sex and age. Diminished cell count, membrane integrity and altered hydration status in critical illness leads to a decreased PhA, which has been shown to correlate with increased mortality, length of ward-, ICU-and hospital-stay, duration of mechanical ventilation and APACHE-II score in various diseases [2].…”

Erfassung und apparatives Monitoring des Ernährungsstatus von Patient*innen auf der Intensiv- und Intermediate Care Station

“…Unter Einbeziehung des Körpergewichts können über verschiedene Algorithmen die fettfreie Masse, Körperzellmasse und Fettmasse berechnet werden [ 81 , 82 ]. Diese Berechnungen sind jedoch bei Intensivpatient*innen weit weniger aussagekräftig als der gewichtsunabhängige, jedoch alters- und geschlechtsabhängige Phasenwinkel.…”

Protein requirements and provision in hospitalised COVID-19 ward and ICU patients: Agreement between calculations based on body weight and height, and measured bioimpedance lean body mass

“…Inbody regards FFM and LBM as synonyms, defined as TBW minus non-essential storage fat mass (FM), corrected for hydration status through extracellular/total body water ratio [12]. In this definition, FFM/LBM includes essential fats, such as those stored in organs, the central nervous system and bone marrow.…”

“…The incorporated software then derives LBM through validated regression analyses based on a healthy reference population. BIA derived LBM (LBM BIA ) for calculating protein needs has substantial theoretical advantages over mathematical methods regarding body composition [12]. In addition, BIA measurements can be performed at the bedside, in contrast to other direct methods such as dual-energy X-ray absorptiometry.…”